Unstepped frequency audiometer



Jan. 1, 1929. 1,697,076

H. R. M DERMQTT UNSTEPPED FREQUENCY AUDIOMETER Filed April 27, 1926 Z lllllmllml W 34 In z/en L07",

Patented Jan. 1,1929.

PATENT OFFICE.

mom) a. mus um, or WATERLOO, Iowa.

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Application filed April 27,

My invention relates to improvements in audiometers, and particularly to those which are electrically controlled- One object of my invention is to supply a device of this class capable of being contr'olled to produce evenly variable audible tones in oscillations ranging per second from. 20 up to and beyond the limits of audibility. Another-object is to render it possible by means of the controls of said device to produce and hold any plurality of such oscillations per second within the range of audibility, while controlling the volume or in tensity of the tones down to the Weakest possible intensity audible by any given person.

The above objects are attained by the, employment of. the means illustrated in the accompanying diagram, as hereinafter described and claimed.

Hitherto devices such as tuning forks in, a series of differing pitch capacity have been used for testing hearing, but these are necessarily limited to toneswhich' are widely separated by steps in pitch or intensity, leaving omitted tones therebetween which render them insuflicient in the proper continuously variable testing of audibility as to complete range. v

Audiometers, electrically controlled, have been supplied but also fail in perfection because the controlling means thereof operate by steps in functioning, whereby also there. are gaps produced in the numbersof oscillations or pitch, which is unsatisfactory in practise.

My device is therefore arrangedto avoid these inconveniences, by being controllable to cover the complete range of audible oscillations or pitch per second-by variation either Way evenly and without breaks or steps-in: termittently, so that a perfect control of audiofrequencies is attained in practice.

' With the above objects in view, and it being understood that modifications may be made in the features of the illustrative diagram submitted herewith without departing. from the invention, I have supplied a device including a plurality of circuits, A, B and G, whiclflcooperate'to efiect the above desired.

results.

Referring to the accompanying diagram, the "circuit 5A] is an oscillator inductively coupledcircuitwith both inductance and capacity, so arranged as to generate a fixed frequency' well .above audibility and having at its own .13" battery supplyofelectric our- 1926. Serial No. 104,951.

rent for the plate 12 of the oscillator tube 9. The circuit B'is similar to-A, but has a variable capacity or condenser 11 instead of the fixed condenser 11 of A, for generating variable frequencies, also above audibility, and

having its own B battery: supply at 10. Aside from the above it will be seen that both of the circuits A andB have the same components,

such as the induction-coils 6, 7, and 6 and 7 the inter osed induction coils 8 and 8; and the oscillator tubes 9 and 9, with their plates, grids and filaments 12, 13 and 14, and 12, 13 and 1 respectively. The circuit B contains in its grid line 35 the resistance 33 and condenser 34 as a grid leak.

The circuit C is an ordinary detector one, containlng the detector 18 with its plate, grid andfilament 19, 20 and 21; its A battery at 22 with conductor 15 connected to the filaments 141 and 14; and a voltmeter 23 connectedacross the filament at 15 to the part 15' of the conductor 15. In the C circuit, a

conductor 16 leads from the detector grid 20 to the respective induction coils 8 ,and 8 of the circuits A and B, including a condenser 27 and a resistance 26. A conductor 17 is in' circuit between the battery 10 and the conductor 31 leading'to the ear-phones 32, in-

cluding a condenser 30 and a resistance 29,

produ'ced in the receiver 32.

The circuits A and B, being both regenerative, are when closely associated, preferably inclosed in separate copper compartments": 1 and 2'respective1y, which shield them from eachother as to interference, the conductors which issue from each being further protected by like partition we at 3, 4, 5, 36 and 37 When the circuits A and B are oscillating at the same frequency, there are no oscillations picked up by the induction coils 8 and 8 andc'onsequently. no differential impulse detected by the'circuit G. However, when the circuit B is tuned at a higher or lower frequency than the circuit A,,the induction coils pick-up the'beat'caused by this difference, whereby thefrequencyof the oscillation is equal to the difference in frequencies of circuitA and circuit B. This oscillation being picked up by the detector 0 and passing through the ear-phones32, produces a tone the range of audio frequency, 'is therefore audible It"will be seen that any tone whatever claim as new B Patent, is:

, and desire to secure by I etters An audiometer comprising a detector c1rcuit inductively cou led with two circuits of.

higher than audio requency, the latter circuits respectively including fixed and variable condensers, whereby variations caused -to be produced in the variable condenser originate non-stepped heterodynes in the dctector circuit.

In testimony whereof I affix my signature.

HAROLD R. MCDERMOTT. 

